This invention relates to protective thermal barrier layers and, more particularly, to abradable ceramic thermal barrier layers and methods of manufacture.
Components that are exposed to high temperatures, such as a component within a gas turbine engine, typically include protective coatings. For example, turbine blades, turbine vanes, and blade outer air seals typically include one or more coating layers that protect the component from erosion, oxidation, corrosion or the like to thereby enhance durability and/or maintain efficient operation of the engine. In particular, conventional outer air seals include an abradable ceramic coating that contacts tips of the turbine blades during engine operation such that the blades abrade the coating upon operation of the engine. The abrasion between the coating and the blade tips provides a minimum clearance between these components such that gas flow around the tips of the blades is reduced to thereby maintain engine efficiency. Typically, the coating is formed using a thermal spray process or the like to deposit and securely bond the coating on the component.
One drawback of the abradable ceramic coating is its vulnerability to erosion and spalling. For example, spalling may occur as a loss of portions of the coating that detach from the component. Loss of the coating increases clearance between the outer air seal and the blade tips and is detrimental to turbine engine efficiency and/or the durability of the air seal itself. One cause of spalling is the elevated temperature within the turbine section, which causes sintering of the ceramic coating. The sintering causes the coating to shrink, which produces stresses between the coating and the component. If the stresses are great enough, the coating may delaminate and detach from the component.
Accordingly, there is a need for a thermal barrier layer having enhanced thermal resistance to decrease or avoid spallation due to sintering shrinkage, and a method of manufacturing such a thermal barrier layer. This invention addresses those needs while avoiding the shortcomings and drawbacks of the prior art.